Manufacture and production of caustic soda



Ratented 8, 1924.

soasms TED STATES PATENT OFFICE.

momma ownN JONES, or ORICKLEWOOD, LoNnoN, ENGLAND, ASSIGNOR 'ro coua'rruzrnnsv LIMITED, or LoNnoN, ENGLAND, a comrANY or can BRITAIN.

mANUrncruaE AND raonucrroNor caosrrc sons.

No Drawing.

To all whom it may concern:

. Be it known that I RICHARD OWlIN J oNEs, v

London, England, have invented new and useful Improvements in or Connected with the Manufacture and Production of Caustic Soda, of which the following is a specification.

The usual methods oi preparing caustic soda on a manufacturing scale from sodium carbonate by means of lime, rarely produce solutions of higher concentration than 8 per cent. It has long been known that the .reaction 1s reversible, and that the higher the concentration of the sodium carbonate the lower will be the. roportion converted into caustic soda. onsequently, it has been the practice to work towards solutions of approximately 8 percent strength givin a conversion of about '92 per cent of t at theoretically obtainable. Many attempts have been made to raise this equilibrium point so that more concentrated solutions of equal purity could be prepared, but hitherto these attempts have been without success.

' According to the present invention, solutions containing up; to about 20 'percent of caustic soda can be obtained. v

' When solutions of increasing concentra-' tion of sodium carbonate are'causticized, the concentration of the caustic soda eventuall reaches a limit,-.after which further addition of sodiumcarbonate has no effect upon the yield ofvthe caustic soda, anyexcess of sodium carbonate added-over and above' this limit of concentratiou'bein thrown out of solution in the formof t e insoluble double com und of calcium carbonate and sodium-car onate. If, however, theliquor be se arated by filtration from the recip ltate calcium carbonate, and the sai ,liquor be, treated with an additional quantity of sodium carbonate and lime, a further conversion to caustic soda takes place,' the equivalent quantity of the insoluble double compound of sodium carbonate and calcium carbonate being formed at the same time.

In this process, therefore, the causticizing formed, but the invention is not imite proximately 14.5 er cent of caustic Application filed June 9, 1922. Serial). 567,201. k u

is carried out in two stages, as represented by the followln'g equat1ons:--

(I) Ca(0H):+Na:OOa?22NaQH+-Ca6()- (II) 'ouomfizmacoa rzmom mon+Nmooaoacoamo In. the first sta the-concentrations are so chosen that litt e, or none, of the aforesaid double carbonate compound is formed and, after the completion of this stage, the liquor isfiltered from the recipitate, which consists mainly of calcium carbonate and in the second 'sta e more sodium carbonate and lime are adde to this liguorwhen a further conversion to caustic so a takes place in accordance with the foregoing equation II.

In this manner a liquor 1s readily obtained containing about 20 per cent caustic soda and about 6 per cent sodium carbonate.

The aforesaid double compound after se aration, for. instance, by filtration, is read ly decomposed by means of water furnishing a solution of sodium carbonate which can be employed for the production of canstic soda. I

The following is an example'of themanner in which this invention ina be. er-

to this example. The parts are by weight.

660 arts-of sodium carbonate are dissolved in 2000' parts of water and \the solution heated to 90 centigrade. The liquor is stirred whilst 300 arts of quicklime areadded gradually t e heat of the reaction being suflicientto maintain the requisite temperature. When the reaction has subsided, the heatin is continued, the mixture being kept boi ingfor an hour, keeping th'e'volume ap roximately constant. The resulting solution as a specific gravit of at least 1.225.. The liquor is filtered o from the calcium carbonate and contains a a and 7.8 per cent 0 carbonate.

12 parts of sodium carbonate are added to each parts ofthe hot filtered 1i uor and the causticizing is carried out, in t 0 manner hereinbefore described, by the addition of- 4 parts, of 'quicklime and boiling for one hour. The mixture is stirred whilst cooling to between 20 and. 30 centigrade. The

resulting solution has a specific gravit of at least 1.25. Thehquor separated rom the preci itate containing the double carthe rate of cooling of the liquor. l r I What I claim is A 1. The manufacture of comparatively concentrated solutions of caustic soda fromsodium carbonate by 'causticizin with lime as completely as possible a so ution containing about 'er cent of sodium carbonate, then filtering off the liquor, then dissolving in this liquor about a further 10' 16, per cent of sodium carbonate, and then cau'sticizin the solution again as complete- \ly as pos'si 1e withlime, whereby, on cooling, a liquor is obtained which contains at 1,,eea

ins approximately 660 -parts by weight, of so ium carbonate in approximately- 2000 parts,'by weight of water, heating the solution, stirrin .into it approximately 300 each 100 parts, by weight, ofthe hot' liquor, and approximately 4 parts, by weight, of

quicklime boiling the mixture, followed by cooling w ilst stlrring, and then separating the liquor from the precipitate. .-'.1 I

In testimony whereof I have signed my name to this specification in thepresence of two subscribing witnesses.

least 18 'per cent of caustic soda and some RICHARD 'JO -EJ 20 sodium carbonate. I Wit a a 2. The manufacture of caustic soda from "SIDNEY S. WAPPER,

sodium carbonate which comprises dissolw- GIBERT me; 

